Known supporting structures of vehicle seats have structural or retaining parts which are stamped out of thin sheet steel and welded together. In the case of motor vehicle seats, identical material pairings are almost exclusively welded together, for example steel with steel. However, this increases the overall weight of vehicle seats, which is undesirable.
It is possible to reduce the overall weight of vehicle seats by using lighter materials. However, in this respect it should be noted that on the one hand, structures of vehicle seats are to comprise materials with a high weight-specific rigidity, strength and energy absorption to increase the safety of the occupants, while on the other hand lightweight materials are to be used to reduce the overall weight.
The different materials of such hybrid structures have to be joined together in a suitable manner. Adhesive bonding, riveting, screwing or clinch-riveting are known from the prior art as joining methods.
FIG. 1a is a schematic side view of a backrest frame 104 according to the prior art which comprises two backrest frame side parts 114, on the lower end of which a respective metal fitting 108 is attached for connection with a seat frame (not shown). According to FIG. 1a, the metal fitting comprises an upper connection part 109a fixed to the seat side part and a lower connection part 109b fixed to the seat side part which are connected together by screws or rivets 124. Holes 123 are provided in the lower connection part 109b fixed to the seat side part for connection with the seat frame (not shown) by screws or rivets. The upper end of the metal fitting 108 is connected to the backrest side part 114 by screws or rivets 118.
FIGS. 2a and 2b show a further backrest frame and a seat frame of a vehicle seat according to German Utility Model DE 20 2007 005 182 U1 of the Applicant. The two frame parts 104, 106 comprise an encircling supporting frame 110 which ensures the necessary stability for the vehicle seat. Provided in the connection region, i.e. in the lower region of the backrest frame 104 and in the rear region of the seat frame 106, is a respective crossbar 112 which interconnects in each case two edge side cheeks 114. The metal fitting 108 is provided to interconnect the two frame parts 104, 106. The seat frame 106 further comprises a rail guide 116 with an upper rail and a lower rail, which rail guide 116 is rigidly connected to the floor of the vehicle, it being possible for the upper rail to be moved in the lower rail to adjust the seat lengthways in the longitudinal direction (X-direction). The metal fittings 108 are preassembled on the backrest frame side cheeks 114 by screws or rivets 118. The holes 123 in the lower end of the metal fittings 108 are used to connect the metal fittings 108 to the seat frame 106 by screws or rivets. However, the connection portions provided for connection using screws or rivets must be relatively large since high-strength connection methods are required for crash optimisation. This increases the weight and the production costs of a vehicle seat. In addition, screwing or riveting is a relatively laborious procedure.
For joining two different metals, welding processes are also known from the prior art which are basically divided into welding processes which do not use pressure and welding processes which do use pressure. Examples of a welding process without pressure (fusion welding) are metal-active gas welding or laser welding known from the prior art. However, these welding processes are relatively complex and are often unsuitable where there is a lack of space.
EP 1 321 218 B1 discloses such a method for joining different types of connections of two different materials, namely aluminium or an aluminium alloy and steel or coated steel, using an electric arc under an inert gas atmosphere formed from a specific gas mixture.
EP 1 806 200 A1 discloses a method for joining an iron-based element to an aluminium-based element, in which a layer of zinc is applied to a joining surface of at least one of the elements to be joined to the other, which layer becomes plastic during welding in order to join the elements together. Resistance welding, laser welding, electron beam welding or arc welding are disclosed as welding processes.
For joining two different metals, welding processes which use pressure (pressure welding) are also known from the prior art, examples being seam welding, projection welding or spot welding. In these processes, the parts to be joined together are interconnected in a plastic but unmolten state. However, with the exception of ultrasound welding, these welding processes are not known in the vehicle seat sector.
In the following, examples are given of such methods for welding different material pairings, some of which are also used in motor vehicle construction.
WO 93/10935 discloses a method for joining parts by friction stir welding. EP 1 400 302 A1 and EP 1 884 308 A1 disclose further methods for friction stir welding.
EP 0 513 646 B1 discloses a method for joining blanks and construction parts made of steel to those made of aluminium in the production of turbines, the blanks or parts being joined together with the insertion of at least one transition layer made of a ductile subgroup metal and, to join parts made of steel to parts made of aluminium alloy, a pure nickel layer is applied to the steel by friction welding, the worked-off surface of the pure nickel layer is joined with the aluminium alloy by friction welding, or to join parts made of steel to parts made of titanium alloy, a copper layer is applied to the steel by friction welding and a vanadium layer is applied to the titanium alloy by friction welding and the machined copper and vanadium surfaces are joined together by friction welding.
DE 103 93 368 T5 discloses a laser roll welding method for different metals to join together a first metal sheet and a second metal sheet of different materials which are kept in a state of non-contact, in which method after only the first metal sheet has been heated by laser irradiation, a heated portion of the first metal sheet is pressed against the second metal sheet by a pressure welding roller so that they are brought into firm contact with one another and are subjected to plastic deformation, and a joining portion between the first metal sheet and the second metal sheet is cooled.
In the motor vehicle seat sector, laser welding, spot welding and projection welding are used as welding methods.
German Utility Model DE 20 2007 009 701 U1 discloses a structure of a vehicle seat, comprising at least two structural parts of different materials which are joined together in at least one contact point by means of ultrasound welding. At least one of the structural parts can consist of aluminium or of an aluminium alloy and the corresponding joining partner can consist of steel or, alternatively, at least one of the structural parts can consist of a fibre-reinforced plastics material and the corresponding joining partner can consist of aluminium, an aluminium alloy or steel. In the confined spaces encountered with vehicle seats, it is not always easy to connect adequate power via ultrasonic transducers. This can also increase the costs for a flexible production.